315 



parapophysis. An inferior spine U dereloped from the centrum of each cervical vertebra, 

 except the atlas, which sends off two diverging processes (hypapophyses) from iu inferior 

 H**T The first rib developes small tubercle, which U articulated to the diapopophyntflf 

 the first dorsal vertebra ; iu head articulate* to the interspace between the firnt donal and 

 last cervical vertebne : the second rib is similarly articulated, but by a still shorter tubercle : 

 the ""Dining ribs articulate by their head alone to the vertebral interspaces, except the last 

 (seventeenth), which is supported exclusively by the centrum of the seventeenth dorsal ver- 

 tebra. The luemapophyses of the second to the sixth dorsal vertebne inclusive are owified, 

 and are joined by short cartilaginoiu bars to the pleurapophysea, but articulate directly with 

 their hamal spines or sternal bones. The ilium articulates with a strongly developed lower 

 transverse process (parspophysis) of the first sacral vertebra, and by a part, answering to 

 the tubercle of a rib, with the upper transverse process of the same vertebra, a space or 

 foramen being thus circumscribed in the same manner as the vertebral foramen is formed in 

 the axis vertebra : the part of the ilium corresponding with the head of the rib also arti- 

 culates with part of the parapophysis of the second sacral vertebra. The latter processes 

 are well developed in all the caudal vertebne. Coalescence is nearly complete between the 

 scapula- and coracoids : the clavicles and rpistenmm are distinct. The manubrium iterni 

 is divided by a median harmonia. The capsular ossicle of the shoulder-joint is distinct, and 

 attached to the proximal epiphysis of the humerus. 



Presented by George Bennett, Esq., F.L.S. 



1099. The skeleton of the Platypus, or Duck-mole (Ornithorfiynclms paradorut). 



All the cranial sutures are obliterated in this mature specimen. The skull articulates with 

 the atlas, as in all Mammalia, by two condyles developed from the cxoccipital elements. 

 There is a circular notch which is almost a complete foramen above the foramen magnum, 

 the plane of which is nearly vertical. The premaxillary bones are broad, flat, and diverge, 

 with their extremities bent towards each other, but without meeting. The broad and flat- 

 tened extremities of the mandibles similarly diverge, but to a less degree. There are two 

 broad and shallow sockets at the back part of the maxillaries, and two below in the corre- 

 sponding parts of the mandibles for the horny grinding teeth : the floor of the alveolus is 

 cribriform, for the passage of the vessels and nerves to the matrix of the tooth. Tin- man- 

 dible articulates by a convex condyle on each side to the base of the squamosal. The atlas 

 has two broad transverse processes and two strong hypapophrses, but no upper spine. Tin- 

 axis is chiefly remarkable for the persistence of the articulation between its broad and short 

 rib and its upper and lower transverse processes. The ribs of the succeeding cervical* are 

 here anchylosed to their respective vertebne : they progressively diminish in size, as do like- 

 wise the spinous processes of the cervical vertebne, which are seven in number and have no 

 xygapophyses. The eighth vertebra has its ribs or pleurapophyses moveably articulated with 

 it, and the inferior or hsemal arch is completed by bjemapophyses which articulate with a 

 broad tuemal spine or first bone of the true sternum. This character of the eighth vertebra 

 or segment establishes the commencement of the dorsal region in all Mammalia, and this 

 region terminates with the last vertebra supporting moveable ribs. There are 1 7 dorsal ver- 



SiS 



